Palladium and palladium alloy nanoparticles can be used as catalysts, particularly in fuel cells used to produce electrical energy. For example, in a hydrogen fuel cell, a palladium catalyst can be used to oxidize hydrogen gas into protons and electrons at the anode of the fuel cell. At the cathode of the fuel cell, the palladium catalyst triggers the oxygen reduction reaction (ORR), leading to formation of water.
Fuel cell performance depends in part on the available surface area of the palladium nanoparticles. Fuel cell performance generally increases when the surface area of the palladium nanoparticles is increased. In addition to size, the shape of the palladium nanoparticles can also be selected in order to further increase the oxygen reduction reaction (ORR) activity. Surfactants are commonly used during nanoparticle formation to control the particle size and shape. The surfactants bind to the nanoparticles as they are shaped and sized.
Once the nanoparticles have been formed, the surfactants used for shaping and sizing the particles need to be removed. Some surfactants can be removed by washing and low temperature heat treatment. Other surfactants, however, require long washing times (as long as weeks in special solvents) or high temperature treatment at temperatures above 300° C. For some catalyst nanoparticles, high temperature treatment presents problems. For example, at 300° C., cubic palladium nanoparticles may lose their shape and increase in particle size. As a result, using high temperature treatment to remove surfactants from the nanoparticles removes benefits the surfactants were intended to provide.